Someone gave me a Fluval 305 a couple of weeks ago. He had used it for 3 months and decided it was too much work. I didn't realize it still had water and all the media still in it. I have no idea about this guys tanks so am worried that there might be something in the filter that might harm my fish. Can I clean it with bleach? I am moving the media from my 204 and putting in new media. Can I clean the impeller housing with bleach also?